Obesity has reached epidemic proportions in western societies. However, mechanisms contributing to its pathology are incompletely understood, and, treatment options remain limited. Our goal is to evaluate a novel approach, antibodies that inhibit tissue factor (TF) signaling, in the treatment of obesity and the metabolic syndrome. In addition to its procoagulant role, TF has coagulation-independent functions in inflammation and angiogenesis. Thus, binding of VIIa to TF also leads to direct signaling via the G-protein coupled protease activated receptor-2 (PAR2). The high fat diet (HFD) fed C57BL/6J mouse model of obesity simulates the human condition, including feeding behavior (hyperphagia), weight gain/energy metabolism, and the development of the metabolic syndrome characterized by insulin resistance and type 2 diabetes. We show that TF and PAR2 are co expressed in adipose tissues (AT) and elevated in adipose tissues of HFD-induced obese mice. Moreover, mice lacking the cytoplasmic domain of TF (TF4CT mice) or PAR2 are protected from HFD- induced obesity and the subsequent development of insulin resistance. In obese wild-type mice, an antibody that blocks TF-VIIa binding rapidly improves insulin resistance. Insulin resistance was also ameliorated in obese transgenic mice that express human TF when they were treated with a monoclonal antibody that specifically blocked TF signaling. The overall goal of this grant is to characterize the contributions of TF signaling to the pathogenesis of obesity with the long term goal to advance a rational pharmacological targeting of this pathway to combat obesity and its complications. In Aim 1 we will use Wild type, TF4CT , PAR2-/-, and double deficient TF4CT /PAR2-/- mice together with bone marrow (BM) chimeras and adipocytes isolated from these knock-out mice to characterize the contribution, cellular targets and mechanisms by which TF-VIIa- PAR2 signaling supports the development of obesity. In Aim 2 we will use a variety of approaches including BM chimeras of TF4CT and PAR2-/- mice and isolated AT macrophages to validate that macrophage TF-PAR2 signaling contributes to adipose inflammation and insulin resistance. In Aim 3 we will characterize the mechanism and efficacy of anti-TF treatment strategies in reversing obesity and insulin resistance. Evaluating the effect of monoclonal antibodies that selectively inhibit direct TF-VIIa-PAR2 signaling in transgenic mice expressing human TF will determine the therapeutic potential of such a strategy that carries minimal risk of bleeding complications. These studies will provide fundamental insights into the role of TF signaling in obesity, and test an innovative therapeutic approach in these pathways to improve metabolic complications of obesity. PUBLIC HEALTH RELEVANCE: Obesity has reached epidemic proportions in the US, and with it there is an increasing rise in obesity-mediated health complications including insulin resistance, type 2 diabetes and cardiovascular disease. In spite of this, the molecular changes that promote these disorders are still poorly defined. Our research aims to understand the role played by tissue factor signaling via protease activated receptor-2, proteins involved in clotting and inflammation, in the pathogenesis of obesity and the metabolic syndrome.